This has been an issue especially in things like the Disneyland stream where the twins start back-and-forthing about unrelated things. Maybe there could be an internal message sent to them every now and then that reminds them. Like "You're in Disneyland! Look at the cool stuff!"
Reducing the weight of things the other twin says might also help if that's possible.
It was a cool idea for the girls, but we watch the streams for the them, not to hear about Disneyland or Mickey Mouse or whatever. The Disneyland stream was fine.